An expert witness, particularly in common law countries such as the United Kingdom, Australia, and the United States, is a person whose opinion by virtue of education, training, certification, skills or experience, is accepted by the judge as an expert. The judge may consider the witness's specialized opinion about evidence or about facts before the court within the expert's area of expertise, to be referred to as an "expert opinion". Expert witnesses may also deliver "expert evidence" within the area of their expertise. Their testimony may be rebutted by testimony from other experts or by other evidence or facts.
A witness is someone who has knowledge about a matter. In law a witness is someone who, either voluntarily or under compulsion, provides testimonial evidence, either oral or written, of what he or she knows or claims to know.
In United States federal law, the Daubert standard is a rule of evidence regarding the admissibility of expert witness testimony. A party may raise a Daubert motion, a special motion in limine raised before or during trial, to exclude the presentation of unqualified evidence to the jury. The Daubert trilogy are the three United States Supreme Court cases that articulated the Daubert standard:
Crawford v. Washington, 541 U.S. 36 (2004), is a United States Supreme Court decision that reformulated the standard for determining when the admission of hearsay statements in criminal cases is permitted under the Confrontation Clause of the Sixth Amendment. The Court held that cross-examination is required to admit prior testimonial statements of witnesses who have since become unavailable.
Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993), is a United States Supreme Court case determining the standard for admitting expert testimony in federal courts. The Daubert Court held that the enactment of the Federal Rules of Evidence implicitly overturned the Frye standard; the standard that the Court articulated is referred to as the Daubert standard.
The law of evidence, also known as the rules of evidence, encompasses the rules and legal principles that govern the proof of facts in a legal proceeding. These rules determine what evidence must or must not be considered by the trier of fact in reaching its decision. The trier of fact is a judge in bench trials, or the jury in any cases involving a jury. The law of evidence is also concerned with the quantum (amount), quality, and type of proof needed to prevail in litigation. The rules vary depending upon whether the venue is a criminal court, civil court, or family court, and they vary by jurisdiction.
A Drug Recognition Expert (DRE) is a law enforcement officer trained to identify people whose driving is impaired by drugs other than, or in addition to, alcohol . All DREs follow the same 12 step procedure called a Drug Influence Evaluation (DIE), to determine which category of drugs is causing the driver to be impaired.
Admissible evidence, in a court of law, is any testimonial, documentary, or tangible evidence that may be introduced to a factfinder—usually a judge or jury—to establish or to bolster a point put forth by a party to the proceeding. For evidence to be admissible, it must be relevant and "not excluded by the rules of evidence", which generally means that it must not be unfairly prejudicial, and it must have some indicia of reliability. The general rule in evidence is that all relevant evidence is admissible and all irrelevant evidence is inadmissible, though some countries proscribe the prosecution from exploiting evidence obtained in violation of constitutional law, thereby rendering relevant evidence inadmissible. This rule of evidence is called the exclusionary rule. In the United States this was effectuated federally in 1914 under the Supreme Court case Weeks v. United States and incorporated against the states in 1961 in the case Mapp v. Ohio, both of which involving law enforcement conducting warrantless searches of the petitioners' homes, with incriminating evidence being descried inside them.
R v Stillman [1997] 1 SCR 607, 1997 SCC 32 was a leading decision of the Supreme Court of Canada on section 24(2) of the Constitution of Canada which allowed for the exclusion of evidence that is obtained in a manner that infringes the Charter. The two-step Stillman test was developed for determining whether the admission of evidence that was obtained through a breach of a Charter right would affect the fairness of the trial. The issue of trial fairness comes into play when applying the first step of the Collins test to exclude evidence under section 24(2).
R v Khan [1990] 2 SCR 531 is a landmark Supreme Court of Canada decision that began a series of major changes to the hearsay rule and the rules regarding the use of children as witnesses in court. In this case, and subsequently in R v Smith (1992), R v B (KG) (1993), R v U (FJ) (1995), R v Starr (2000), and finally, R v Khelawon (2006), the Court developed the “principled approach” to hearsay, where hearsay statements can be admitted if they are sufficiently reliable and necessary.
Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999), is a United States Supreme Court case that applied the Daubert standard to expert testimony from non-scientists.
R v Starr [2000] 2 SCR 144 is a leading Supreme Court of Canada decision that re-evaluated several principles of evidence. In particular, they held the "principled approach" hearsay evidence under R v Khan and R v Smith (1992) can be equally used to exclude otherwise admissible hearsay evidence. In addition, the Court examined the judge's charge to the jury on the standard of beyond a reasonable doubt.
R v Béland [1987] 2 S.C.R. 398 is a leading Supreme Court of Canada decision where the Court rejected the use of polygraph results as evidence in court.
Graat v R, [1982] 2 S.C.R. 819, is the leading case decided by the Supreme Court of Canada on the admissibility of opinion evidence. The Court held that lay persons may give opinion evidence, which is normally reserved only for expert witnesses, where the opinion so closely infers fact that it is a "compendious statement of fact". The determination is left to the discretion of the trial judge.
R v Mohan1994 CanLII 80, [1994] 2 SCR 9 is a leading Supreme Court of Canada decision on the use of expert witnesses in trial testimony.
The hearsay provisions of the Criminal Justice Act 2003 reformed the common law relating to the admissibility of hearsay evidence in criminal proceedings begun on or after 4 April 2005.
Relevance, in the common law of evidence, is the tendency of a given item of evidence to prove or disprove one of the legal elements of the case, or to have probative value to make one of the elements of the case likelier or not. Probative is a term used in law to signify "tending to prove". Probative evidence "seeks the truth". Generally in law, evidence that is not probative is inadmissible and the rules of evidence permit it to be excluded from a proceeding or stricken from the record "if objected to by opposing counsel". A balancing test may come into the picture if the value of the evidence needs to be weighed versus its prejudicial nature.
In eyewitness identification, in criminal law, evidence is received from a witness "who has actually seen an event and can so testify in court".
Opinion evidence refers to evidence of what the witness thinks, believes, or infers in regard to facts, as distinguished from personal knowledge of the facts themselves. In common law jurisdictions the general rule is that a witness is supposed to testify as to what was observed and not to give an opinion on what was observed. However, there are two exceptions to this rule: expert evidence and non-expert opinion given by laymen which people in their daily lives reach without conscious ratiocination.
The role of expert witnesses in English law is to give explanations of difficult or technical topics in civil and criminal trials, to assist the fact finding process. The extent to which authorities have been allowed to testify, and on what topics, has been debated, and to this end a variety of criteria have evolved throughout English case law.
